This invention relates to a method for determining the degree of contamination of liquids, particularly the level of metal contaminants in liquids such as hydraulic fluids and lubricating oil.
Wear at the interface between moving parts is a normal characteristic of machine operation. The kind and the rate of wear depend on the machine. Lubrication is normally provided between moving surfaces to minimize the wear. During operation millions of minute wear particles, ranging in size from submicron to 100 .mu.m or larger, enter the lubricating oil.
It has been long recognized that a knowledge of the quantity and of the rate of increase in the quantity of contaminants in a lubricating oil or hydraulic fluid can give valuable insight into the condition of the machine. Because the quantity of such material is extremely small in a machine in good condition, it has been necessary to employ sophisticated techniques to analyze the oil or fluid.
Atomic absorption spectrophotometric (AAS) and atomic emission spectrometric (AES) techniques have been used for the determination of wear metals in used lubricating oils. Although spectrometers perform a rapid analysis of wear metal particles, the accuracy of the analysis is particle-size dependent. To enable the spectrometers to perform particle size independent analyses, ensuring accurate component wear evaluations, procedures have been developed which incorporate acid dissolution of the metal particles before spectrometric analysis. The most useful of such procedures is a rapid, multielement particle size independent method (PSIM) which is effective for Al, Cu, Fe, Mg, Mo, Ni, Sn and Ti in synthetic ester base lubricating oils (Brown, J. R., Saba, C. S., Rhine, W. E. and Eisentraut, K. J., Analytical Chemistry, 1980, 52, 2365).
The present invention provides an improved particle size independent method for determining the degree of metal wear contamination of liquids. The method of this invention is applicable to all liquid lubricants or hydraulic fluids, the recoveries of Al, Cr, Cu, Fe, Mg, Mo, Ni, Pb, Si, Sn, Ti and Zn are quantitative and recoveries for Ag, Cd and Na are greatly improved, and the reaction time and temperature are considerably reduced.
Accordingly, it is an object of the present invention to provide an improved method for determining the degree of wear metal contamination of liquids.
Other objects, aspects and advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed disclosure.